Age-related differences in the speed with which children, adolescents, and adults execute mental processes are ubiquitous and large. These age differences have been linked to a global mechanism (i.e., one that is not specific to particular tasks or domains) that changes exponentially with age. The long-term objective of the present project is to characterize this mechanism and understand its Impact on cognitive development. The specific aims of the present research are these: (1) The proposed work will examine a connectionist theory in which performance involves multiple processing steps. Some information is presumed to be lost at each step in the network, and the degraded signal that results is processed more slowly. According to the model, children process information more slowly because more information is lost per step, which means more time is consumed at each step waiting for sufficient information to accrue to identify the signal. The theory will be examined in experiments in which feedback is used to manipulate accuracy and degraded stimuli are presented. (2) Most work on developmental change in processing speed has focused on 7- to 22-year-olds, which means that claims that a global mechanism underlies developmental change in processing speed must be restricted to this age range. Included in the proposed research are methods that would allow younger children to be tested, thereby providing a stronger test of claims concerning the global mechanism. These methods involve examining the relation between children's and adults' mean response times across different experimental conditions. (3) Young children often are initially incapable of executing some cognitive process but can do so when information is presented more slowly. In these cases, sufficient time to execute processes has been determined on an ad hoc basis. An aim of the proposed work is to use research on processing speed to predict sufficient presentation rates for children to execute particular cognitive processes. The method involves, first, determining presentation time-performance functions at different ages, and, second, examining developmental change in the presentation time that is sufficient for individuals to perform various tasks.